Predicting interrill erodibility factor from measured infiltration rate

Direct measurement of an interrill erodibility factor ( K i ) is costly and time intensive. As K i and the final infiltration rate (FIR) under seal formation are both affected by aggregate breakdown at the soil surface, it was hypothesized that the K i and FIR values are correlative. FIR and soil‐loss values of 53 soils, measured in several different laboratory rainfall simulators, were investigated. The slope factor ( S f ) of smectitic soils was higher than that of nonsmectitic soils at slope angle (θ) > 9%. The equation S f = exp (−0.68 + 8.28 sin θ) defines significantly ( r 2 = 0.94) the S f for smectitic soil. For the various soils the FIR and K i values were correlative and fitted significantly the K i = a −b In(FIR) model; a and b are empirical coefficients. This model was found applicable for a wide range of rain intensities (34–68 mm h −1 ). However, an increase of the raindrop kinetic energy from <11.6 to 22.3 J mm −1 m −2 increased the absolute values of the coefficients, a and b . The FIR‐ K i model differed for smectitic and nonsmectitic soils; at a given FIR, the smectitic soils had a higher K i value than the nonsmectitic soils.